Carburizing bath



Patented Feb. 13, 1 951 CARBURIZING BATH Facundo R. Morral, Stamford, -Conn., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine I No Drawingpplication September 14, 1948, i SerialN0. 49,300 v leave an insoluble sludge on the article after it;

3 Claims. (Cl. 148--30) tion gives effective case depths on fracture up to about 33 mils during a four-hour treatment in the bath, and the film of adherent salts after an oil quench is so soluble that it may be removed simply by shaking the work in hot water a .few times. Adherent salts from holes inchin diameter and A2 inch deep are easily removed by a such means.

is removed from the bath, oil quenched, and

shaken in hot water. It is a further object of the present invention to provide an easy washing carburizing bath operable over a temperature range,

of 1550* to 1650 F. It is a still further object to provide an inexpensive, novel, and effective activator for such a bath, namely, a hydrated sodium silicate. Still other objects will be obvious from the description of the invention given below.

A cyaniding bath containing unactivated sodium cyanide does not coat the work with insoluble sludges, but is unsuitable as a carburi'z ing bath because it carburizes slowly and gives eifective case depths of only about 12 mils at the 0.6% C; and about givean effective case depthof from 16 mils in an I hourat 1600 F. to 125 mils in 16 hours at 1750 F. A disadvantage of a bath activated with calcium and barium salts is that these salts sludge, forming oxides and carbonates that adhere to the article when it is withdrawn from the bath and that cannot be dissolved in hot water, but must be removed from the article by chemical and/or mechanical means.

An easy Washing carburizing bath has now been found that incorporates the easy washing characteristics of a cyaniding bath with the high carburizing activity of a calcium salt-activated bath. The bath of the present invention, unlike a cyaniding bath, is operable up to 1650 F. and gives satisfactory case depths even though it contains no alkaline earth activator. The bath of the present invention is further characterized by its high activity in commercial-size pots, its ease of maintaining a good cover, low sodium cyanide loss, and low nitriding.

The bath contemplated in the present inven- When making up the bath, a salt mixture with the following range of ingredients may beused (parts by weight) Suflicierit parts of a hydrated sodium silicate to provide about 3-8 parts of contained S102 Sodium cyanide about 17-25 parts I Sodium carbonate about 25-35 parts I Graphite (or an organic compound serving as binder in briquettes of bath composition) -.3 to 30pm, r

Sodium chloride, remainder of b ath to glue parts total "Various equivalents may be used for the above substances. For example, various other watersoluble cyanogen-forming compounds may be used instead of sodium cyanide, namely, other alkali'metal cyanides, cyanates, cyanamides, and the like. Organic cyanogen compounds are also suitable as, for example, cyanamide, dicyandiamide, melamine, melam, melemf-melon, ammeline, ammelide, hydrogen cyanide polymers, and the like. The sodium carbonate of the-bath may be substituted'for, in total or in part, by other alkali metal carbonates, and the'sodiurn chloride'may. be similarly substituted by other alkali metal chlorides. The hydrous sodium silicate may vary Widely in its NazO:SiOz':I-I2O- ratio and may be replaced by a hydrous potassium siligate. Although the quantity ranges listed above are operable and are contemplated by the invention, the following composition represents the preferred materials and their preferred ranges (parts by Weight) NaCN, 17-20 parts NazSiOafiHzO, 10-15 parts NazCOs, 30 parts Graphite, .3 part NaCl, remainder to give 100 parts total In the following tabulation the performances of various carburizing baths containing hydrated sodium silicates are compared with a bath activated by anhydrous sodium silicate. It will be observed that within certain ranges of silica content, satisfactory case depths, namely 16 to 17 mils, are obtained within one hour. silicates of various NmOzSiOmHzO ratios can be used as the hydrous sodium silicate in the bath. For example, bath B in the following tabulation contains a sodium silicate of the approximate formula Na2O.SiO2.5I-I2O, whereas bath D contains a hydrous sodium silicate of the approximate formula Na2O.'3.4SiO-2.2.9H2O, and bath E contains a silicate of the approximate formula NazO.SiO2.9I-I2O. While any hydrated sodium silicate will provide the desired activation of the bath if present in the quantity suflicient to provide an initial silica content in the bath of from 3-8%', the preferred silicate is sodium meta silicate pentahydrate, because it is the cheapest 15 hydrated silicate on the market,

2. A mixture adapted upon fusion for the carburizing of ferrous metal articles which consists essentially of sodium cyanide 24 parts, sodium carbonate 30 parts, sodium metasilicate pentahydrate 10-15 parts, sodium chloride 40 parts, and graphite .3 part, the parts being by weight.

3. ,A mixture adapted upon fusion for the carburizing of ferrous metal articles which consists essentially of cyanogen compound 17-25 parts, alkali metal carbonate 25-35 parts, hydrous allialisilicate providing about 3-8 parts of contained silica, carbon .1-3 parts, and alkali metal chloride to make 100 parts, the parts being by weight.

FACUNDO R. MORRAL.

Performance of sodium silicate activated carburizing Composition of Startbaths at 160i? 1?.

ing Bath, Per Cent A B C .D E F G H analy i NazO.per 081112,- 23. 3 29. 1 29.1 19. 4 21. 8 29. 1 29. 1 29. 1 S102 dO 75 28. 1 28. 1 62. 5 2-1. 1 28. 1 28. l 28. 1 42. 8 42. 8 17:5 '57. 1 42. 8 42.8 42. 8

2.1) 4. a) (4. 7) I (4. 7 s. 4 e. 4 a. c)

Efiective case depth on fracture in mils alter NaCN 1 ntent oibath has fallen to 17.5%

me H r v A. B G D E F G H Total case depth, microscopic r While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims.

I claim: a

' '1. A mixture adapted upon fusion for the ear-- burizing of ferrous metal-articles which consists essentially of alkali metal chloride 25-45 parts, cyano en compound about 1 2.5 par alkali metal carbonate 25-35 parts, hydrous alkali sili-. cate providing; 3- 8 parts of; contained silica, and carbon .1-3 parts, the parts being by weight.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Beck Dec. 8, 1936 QTI-IER REFERENCES Number 

1. A MIXTURE ADAPTED UPON FUSION FOR THE CARBURIZING OF FERROUS METAL ARTICLES WHICH CONSISTS ESSENTIALLY OF ALKALI METAL CHLORIDE 25-45 PARTS, CYANOGEN COMPOUND ABOUT 17-25 PARTS, ALKALI METAL CARBONATE 25-35 PARTS, HYDROUS ALKALI SILICATE PROVIDING 3-8 PARTS OF CONTAINED SILICA, AND CARBON .1-3 PARTS, THE PARTS BEING BY WEIGHT. 